Nowadays, mobile phone systems have grown higher in transmission rate and more enhanced in functionality. The transmission rate, which was 9.6 kbps or 28.8 kbps before, has recently increased to 384 kbps or 14.4 Mbps, and will be expanded to 30 Mbps or even 100 Mbps in the future. To realize the high transmission rate, the introduction of various technologies including OFDM (Orthogonal Frequency Division Multiplexing) and MIMO (Multiple Input Multiple Output) as well as diversity reception and transmission power control is scheduled.
Under these circumstances, wireless base stations are required to have many functions and high processing capabilities. As a result, there are concerns about increased manufacturing costs and increased power requirements for the development of new wireless base stations.
The present invention is focused on a timing correlator for use in measuring the received timings of signals transmitted from wireless mobile stations in order to simplify the wireless base station. The timing correlator is a functional device for determining a plurality of points (referred to as a delay profile) of cross correlation between a signal having a predetermined pattern and a received signal at shifted timings in order to perform diversity reception and for determining the timing of highest correlation. The timing correlator is also called a path searcher, and is an indispensable functional device for CDMA communication systems for RAKE reception.
Generally, as disclosed in Patent Document 1 (JP-A No. 2003-283373), FIG. 8 and paragraph [0004], the timing correlator has its range of correlation-determining timings widened and its circuit scale increased depending on the radius of an area covered by its wireless base station. This is because wireless mobile stations transmit respective signals at timings of their own and are scattered about in the area, so that they have different propagation delay times to the wireless base station. Should the wireless mobile stations take timings to transmit signals into account, the detecting range of the timing correlator provided in the wireless base station may be held to the minimum required and hence its circuit scale may be reduced.
Patent Document 1: JP-A No. 2003-283373